Introduction to the CohortThe Cardiovascular Health Cognition Study is an ancillary study of the Cardiovascular Health Study (CHS). Beginning in 1989, the CHS is population-based, prospective cohort study of adults aged 65 years or older residing in one of four US communities (Sacramento County, California; Washington County, Maryland; Forsyth County, North Carolina; and Pittsburgh, Pennsylvania). Eligible persons were drawn from the Health Care Financing Administration Medicare enrollment lists by random sampling of three age strata. The Cardiovascular Health Cognition Study began in 1992 when CHS participants were invited to undergo cerebral magnetic resonance imaging (MRI) and participate in cognitive testing. At the 1992 baseline, 3,608 individuals had both the MRI and cognitive testing. 3,375 participants were determined to be free of dementia and were followed for incident dementia for an average duration of 5.4 years (median, 6.0; range, 0.03-8.4 years).